A single crystal of gallium oxide (particularly a β-Ga2O3 single crystal, the following description will refer to a β-Ga2O3 single crystal) has been studied and developed initially for crystal growth thereof as a substrate for producing a GaN thin film for LED since the reports of single crystal growth by the FZ method or the CZ method by Y. Tomm, et al. in 2000 (NPLs 3 and 4).
In recent years, M. Higashiwaki, et al, reported the implementation of an FET for a power device using a β-Ga2O3 single crystal (see NPL 11), and the production of a β-Ga2O3 single crystal with high quality, large size, and low cost for achieving a wide gap semiconductor substrate for a power device is receiving intense interest.
It is considered that a β-Ga2O3 single crystal taking the application to devices into account can be grown by such methods as the floating zone (FZ) method, the CZ method, the EFG method, the VB method, and the HB method, as shown in FIG. 18.
Among these crystal growth methods, the FZ method requires no vessel for retaining a raw material melt due to the crystal growth principle, and therefore the measure for heating the raw material to a high temperature for melting (melting point) can be relatively easily achieved, for which various studies have been made (see NPLs 1 to 3, 5, 7, and 8). However, the FZ method has a technical limitation in providing a large crystal with high quality suppressing structural defects including dislocations, in consideration of the growth principle and the temperature environment thereof, and it can be said that the FZ method does not sufficiently measure up the application to devices although various investigations have been made in recent more than ten years (see NPLs 1 to 3, 5, 7, and 8 and PTL 6).
As a production method of a large single crystal with high quality, capable of being applied to industrial production, the CZ method and the EFG method have been frequently applied to the single crystal growth. As for the growth of a β-Ga2O3 single crystal, it can be expected that active developments have been made since 2000 for the CZ method (see NPLs 4 and 10) and the EFG method (NPL 9 and PTLs 1 to 5). However, a β-Ga2O3 single crystal that has large size and high quality, and is produced at low cost capable of being applied to the future power devices has not yet been provided.